Rather use the source code above and push your modifications as Callable instances into the update queue. The engine allows to implement more or less the traditional approach:
while (!canvas.isClosing()) {
update();
render();
}
If you modify something in another thread while the one on which the OpenGL context is current, bad things might happen and it's not specific to JogAmp's Ardor3D Continuation. It's possible to add some proper synchronization to prevent those bad things from happening but it's not worth it.